The use of the term “overhead door” herein means a door which, when opened, assumes a generally horizontal position and, when closed, assumes a generally vertical position, unless the context clearly dictates otherwise. For readability purposes, the term “trailer” will be used generically herein to refer to both trucks and trailers.
Overhead doors used with trailers are often made using multiple rigid panels. These panels are commonly attached using hinges, allowing for the door to operate within curved tracks. Because these overhead doors commonly utilize multiple hinges, they are often very heavy, requiring the use of a counterbalance mechanism.
Counterbalance mechanisms typically utilize a tensioned spring located at the rear of the trailer, directly above the door opening. The tensioned spring is attached to drum rollers, located on each side of the overhead door, via one or more shafts. A pair of lifting cables is wound about the drum rollers and attach to the bottom, or lowest portion, of the overhead door. By attaching the lifting cables to the overhead door, the tensioned spring aides in lifting the overhead door, by the bottom of the door, resulting in less force being needed to open the overhead door.
Overhead doors used with trailers are often made using multiple rigid panels. These multi-panel doors are commonly attached using a plurality of fasteners (e.g., bolts, screws), allowing for the door to operate within curved tracks. Because these overhead doors commonly utilize multiple hinges, they are often very heavy, requiring the use of a counterbalance mechanism. With a multi-panel door, traditionally, the cables attach to the bottom of the door and will thus lift the multi-panel door from its bottom. By lifting the multi-panel door from its bottom, strain on the hinges (and damage to the multi-panel door) is minimized. If such a multi-panel door was to be lifted from its top end portion, the panels would slightly accordion apart as the multi-panel door is lifted—causing damage to the hinges and their connection points with the panels.